This invention relates to filters. More particularly, this invention relates to a filter of the type having a horizontally fed filter chamber containing loose bulk material as a filter medium and having on the inlet side and on the outlet side a permeable wall for retaining the loose bulk material in the filter chamber and having a compressed-air lift pump for driving the loose bulk material from a funnel disposed beneath the filter chamber in which a bottom lifter is installed from which a standpipe reaches into a rinse chamber above it.
This application claims the priority of German patent application No. 197 04 238.4, filed Feb. 5, 1997, and European patent Application No. 97121109.9, filed Dec. 2, 1997, the disclosures of which are expressly incorporated by reference herein in their entirety.
U.S. Pat. No. 4,399,034 discloses a filter for fluids, wherein the fluid flows through the filter medium at an angle instead of vertically or horizontally. The filter granules contained as the filter medium in a rectangular or cylindrical housing are drawn from the bottom of a hopper and fed for back rinse into a wash zone lying above the filter followed by a distributing apparatus. The outer walls of the filter have slanting slots to let out the fluid, while the fluid to be cleaned is fed through a plurality of stacked inlet cones which are disposed centrally in the bottom part of the filter apparatus. To be able to pump the contaminated filter granules out of the bottom of the hopper, rinse water is pumped into the hopper bottom from the wash zone.
The filter of U.S. Pat. No. 4,399,034 has the primary disadvantage of a very small filter inlet area which forms around the inlet hopper. It is much too small in proportion to the size of the filter outlet area and to the generally large filter volume. In the inlet area the filter medium will therefore very quickly become clogged with impurities, so that the filter resistance increases greatly after a short period of operation. To replace the relatively small amount of filter material in the inlet area a considerably greater amount of less contaminated filter material must be drawn off and necessarily included in the treatment. Another disadvantage results from the fact that the inlet and outlet slots are disposed vertically one under the other. The filter material lying on the slanting slot surfaces is not caught by the vertically descending flowing bed and cakes up, forming a stubborn barrier reducing the free passage area. Both the large bulk of the filter and the various ducts running in and out require a free-standing set-up and accessibility on all sides, which prevents adding the filter onto an existing wastewater pool.
Horizontally swept loose bulk material filters have not as yet been used in wastewater technology, although a horizontally directed flow offers very good conditions as regards the configuration of the filter and its operation, as well as versatility of use.
The present invention is addressed to the problem of creating a horizontally swept filter of the kind named above, which will have the least possible resistance to flow and will not tend to clog even in unfavorable conditions.
This problem is solved by the invention if the hopper has inlet slots close to the bottom and is surrounded by a chamber which is provided with a rinse-water feed tube connecting it to a raw water chamber.
In such a filter the loose bulk material in the lower region of the filter chamber is continuously or periodically drawn off and fed back up to it again. At the same time the loose bulk material is freed of the dirt particles and the rinse water is drawn off separately. The filter is configured to special advantage if the pump in the filter chamber is a compressed-airlift pump for driving the loose bulk material from a funnel disposed beneath the filter chamber through a standpipe and into a rinse chamber above it. Such a pump, often called a "mammoth pump," is especially reliable in operation and in the pumping process it frees the loose bulk material from the impurities that have been filtered out. The compressed-air lift pump requires much fluid in order to drive the loose bulk material, but raw water from the settling tank outside can be used directly. Since the amount of fluid which the compressed-air lift pump discharges is greater than that which can flow back simultaneously through the loose bulk material into the filter chamber, a backup takes place in the rinse chamber which has drain openings arranged at a specific height, through which the raw water contaminated by dirt particles escapes. The filter medium itself, therefore, is not affected by the greater amount of fluid required for carrying the loose bulk material.
A contribution to the further improvement of the purifying action is made when the stand pipe reaches into the bottom lifter and terminates in the rinse chamber where it tangentially adjoins an arcuate turnaround means. By the centrifugal forces it creates, such a deflecting means assists the separation of the loose bulk material from the raw water contaminated with dirt particles. The centrifugal forces produced by such a deflecting means help to separate the loose bulk material from the raw water contaminated with dirt particles.
The filter according to the invention can easily be installed in existing settling tanks without major remodeling if the filter chambers are of modular design and can be disassembled. Thus, by fitting together a plurality of filter chambers any desired filtration capacity can be achieved.
It is quite especially advantageous if the filter chambers or a plurality of assembled filter chambers are disposed as an end wall of a horizontal-flow settling tank for waste water purification. Thus the area of the settling tank downstream from the filter chamber or filter chambers becomes a clean water area from which the filtered waste water can flow from the settling tank on the path already designed without the filter.
Alternatively, however, it is also possible to arrange at the downstream side of the filter chamber a filtrate collecting chamber forming a single unit with the filter chamber. Such an embodiment makes it possible to install the filter of the invention at any desired points in a settling tank, on two lateral walls for example. The filtrate then is produced in the filtrate collecting chamber from which it is to be drawn. At the same time the individual units can be arranged both in tandem to increase the filtering action, and in parallel to increase the throughput. They can easily be fitted into existing systems. An island system for installation in still waters is also easy to create, in which case the filtrate can then be withdrawn upwardly.
The medium to be purified can be fed downward to a round filter exactly as taught in the prior art if, on the input side of the filer chamber a vertical inlet forming one unit with the filter chamber is arranged.
The problem of preventing the escape of filter medium from the two permeable walls without impeding the ongoing replacement of the fill material in the area of the openings can also be solved in the invention by providing the walls with a plurality of openings, one above the other and offset from one another and side by side, each shielded on the inside by an eave-like angle iron above and on the side, the apex of the angle iron pointing upward and its two flanges reaching below the bottom edge of the particular opening. Such eave-like angle irons reliably prevent the escape at the openings of the loose bulk material that does not settle downward and therefore cannot be cleaned and renewed.